Unlike ordinary electric iron products, a garment steamer can be used for direct ironing on garments hanging on the rack, which ignored the trouble of ordinary iron that an ironing board is necessary. When ironing, the steam from the brush head passes though fibers of the ferment and eliminates crimples on the surface, making the garment natural and level; in the meanwhile, strange odors, bacteria and mites are also eliminated due to the high-temperature steam, therefore it is widely used in fashion shops, small clothing factories and some families with high requirements for dressing. At present, most garment steamers on the market are provided with a water tank and heating device inside the main body, water in the water tank flows automatically into the heating device due to the water head, while the heating device is actually an embedded open kettle, which only functions to boil the water to generate steam, due to its structure, an ordinary garment steamer cannot vaporize the steam produced as a steam iron does so as to supply the steam through the steam duct to the brush head for direct ironing; due to the condensation produced when the steam passes the steam duct, the steam coming out from the brush head is generally with high humidity, high temperature and low pressure, which lead to low ironing efficiency and insufficient effect of sterilization and mites elimination. The State Intellectual Property Office of the PRC has disclosed patent application number 200710079302.2 “Steam nozzle and garment steamer containing such nozzle” on Aug. 20, 2008, which added a heating device inside the steam nozzle on the steam panel to heat and vaporize the steam again before being sprayed from the steam nozzle, thus, the condensation water will not be brought out from the steam nozzle and the operation elevation of the steam duct is increased. However, applicant of this patent has found through researches that due to the heating device inside the product, the steam duct and the steam nozzle are connected to the atmosphere, although the steam is vaporized again before being sprayed from the nozzle, the steam generating device still adopts the structure of a kettle, thus, condensation is still unavoidable when the steam passes a long duct; Although the humidity of the steam is lowered, its temperature and pressure are also reduced, therefore, this product still fails to improve the low ironing efficiency and poor effect of mites elimination of most garment steamers.